Regional Differences in Brain Blood Flow During Acute Hypoxemia in the Llama Fetus

The fetal llama, in contrast to fetuses of lowland species, does not increase or increases discreetly total brain blood flow during acute hypoxemia, decreasing brain O₂ delivery. Since the fetal llama maintains cardiovascular function during acute hypoxemia, we postulate that regions of the medulla, involved in cardiocirculatory regulation, could importantly increase the blood flow with maintenance of O₂ delivery. To answer this question 10 fetal llama 0.6-0.7 of gestation were chronically catheterized. Total and regional blood flows (radiolabelled microspheres) and O₂ deliveries were determined during normoxemia (N) and after 45-60 min of severe hypoxemia (H) (<20% SatHb in fetal ascending aorta). The results were (X±SEM; *p<0.05, paired t-test).Table

Table 1

The brain of the llama fetus shows regional differences in blood flows during acute hypoxemia, increasing total brain, pons and medulla blood flows. However, these increases in blood flows are not enough to maintain O₂ deliveries to these regions, suggesting alternative mechanisms to preserve neuronal integrity. FONDECYT 1931033, Chile.